In 1814 Napoleon was finally defeated at the Battle of Waterloo, and Charles was forced into exile as the Austrians annexed the principality. Unable to attend the Congress of Vienna to decide the future of the states of Germany, he was represented instead by his wife Charlotte of Erbach. Despite using all her political clout, Charlotte was unable to secure the principality's future. It was mediatised to Hesse-Darmstadt in 1815. Charles died in 1820 as the last ruling member of Isenburg.